Future Visual focus on multi-user VR and they have their own internal framework for this. Recently the team wondered how they could fuse ARKit and their own VR framework to make a demo with multiple users interacting together using ARKit.
Their demo shows how a user with an iPad can place the environment the VR users are in, onto a surface in the real world, walk around the world to view it from any angle to see what the VR users are doing, and to interact with the scene and users in VR. This creates an Augmented Reality / Mixed Reality window into the VR world.
The main components of the project were:
As the discussion of VR vs AR continues its companies like Future Visual who are pushing the boundaries of bringing them together.
http://www.futurevisual.com/what-we-do/